When a damage or a defect occurs in a joint cartilage due to some cause, it is rare that the joint cartilage is completely restored and regenerated. One of the reasons includes a nature of chondrocyte. That is, as the joint chondrocytes are highly differentiated, scarcely proliferate and differentiate, their restoration capacity is extremely low. Another reason includes a peripheral inherent environment surrounding the chondrocytes. Since a cartilage tissue lacks a nerve and a blood vessel, no restoration mechanism by hemorrhage, inflammation and granulation is available. Since a periphery of the cartilage tissue is surrounded by extracellular matrix, the chondrocytes can not easily migrate from a healthy site to the injured site.
The injured site in the joint cartilage induces degradation of its periphery and adjacent cartilage with time, finally advances to osteoarthritis, and causes the reduction of joint functions, e.g., pain and mobile limitation. Therefore, various therapeutic methods have been developed as methods of restoring the joint cartilage so far, but this is an actual state that the method of restoring a defect site with complete hyaline cartilage has not been well established at present.
Accompanying with the recent advance of cell engineering, regeneration of the cartilage tissue by autologous chondrocytes has been actively attempted. It is important as a transplantation material applied to the injured site that enough amount of the chondrocytes are maintained, and that the retained chondrocytes can produce the sufficient amount of the extracellular matrix.
However, there is a problem that the chondrocytes dedifferentiate into fibroblasts during the culture when the chondrocytes are isolated from an autologous cartilage piece and subsequently grown in a monolayer culture. Thus, it is difficult to culture the chondrocytes keeping with their character well. As a scaffolding exhibiting a three dimensional structure, biomaterials such as collagen gel sponge, agarose gel, gelatin, chitosan, hyaluronic acid and PGA, PLA and PLGA have been reported, but no material having strength and frictional coefficient corresponding to a cartilage matrix has been developed until now, and a transplantation material having the characters close to the joint cartilage tissue has been desired.